Question about Phosphoric Acid

[VaprArts]

I am a graphic Design student at a local community college. My art teacher is also a lithography teacher and he was saying he cannot find an answer to

How long does phosphoric acid stay reactive on aluminum plates. He says he has read from a source that one drip stays reactive for around 2 minutes but the source is not reliable.

Does anyone know anything about this?

 

[Dan Roll]

This is a somewhat vague question, but I'll try to answer it. Acids remain reactive until neutralized. The surface of an aluminum plate may represent a lot of different surfaces, most are anodized, the aluminum has already been oxidized and bonded with a salt of some sort. As many modern emulsions wouldn't stick reliably to these more traditional surfaces, many plates now have even more complicated surfaces. How phosphoric acid would react to them depends entirely on what they are. If you dissolve some baking soda in water and this fizzes when placed on the plate where phosphoric acid has been placed, the acid is still reactive....

 

[Alois Senefelder]

Phosphoric Acid and its role in Litho Platemaking

Phosphoric Acid and its role in Litho Platemaking

Hello fellow Lithographers,


A dilute 1% - 2% or 5% acid/water solution was widely used in the era of Zinc surface plates

and Deep Etch plates, mainly used as a counter etch during the platemaking process.



Regards, Alois

 

[BeauchampT]

Dan Roll has provided the most accurate answer for you. Everything is dependent on what you are comparing. Chances are your teacher is going to have to experiment for himself.....

T